Walter l



UNITED STATES PATENT OFFICE.

WALTER L. GRAUL, OF DETROIT, MICHIGAN, ASSIGNOR TO SEME-T-SOLVAY COMPANY, OF SOLVAY, NEW YORK, A CORPORATION OF NEW YORK.

METHOD OF REGULATING THE QUALITY OF COKE.

No Drawing.

To all whom it may concern:

Be it known that I, WALTER L. GRAUL, a

citizen of the United States, residing at covery of by-products the operation is carried on by sub1ecting bituminous coal to heat in the absence of air. By this means the volatile matter is driven off from the coal and a cellular structureis developed which 7 gives to the coke its special quality as a fuel,

by reason of the presentation of a very large surface for combustion with the oxygen of the air, thereby causing rapid combustion with the consequent production of a high temperature.

While the reason of the coking quality of "coking bituminous coals, as dlstinguished from non-coking coals, is not well understood, it is supposed to be due to the presence in the coal of resinous bodies derived from the vegetable growths from which the coal was formed and that as these bodies meltduring the coking process and the gases generated are driven ofl by the heat, bubbles are formed, the walls of which eventually harden when the volatile matter has been driven off, thus forming the cellular structure of the coke.

Bituminous coals are made up of a mixture of the coking substance mentioned in the foregoing paragraph and a mass of relatively inert matter,mainly fixed carbon and ash. In the coking process the volatile matter in the coal assumes a viscous condition, causing a swelling of the mass and later a shrinkage as the volatile matter leaves the mass, producing more or less violent distortion of the mass, probably thus causing the fissures and crackstwhich occur in the entire mass of coke and in the smaller individual pieces. The inert matter, on the other hand, changes comparatively little, tending to minimize the distorting influence of the volatilizing substance, The quality of the cokeproduced will vary with variations in the relative Proportions of the coking substance andthe inert matter contained in the coal. Thus, if there is an excess of the coking substance in the coal,

Specification of Letters Patent.

Application filed January 7, 1919. Serial No. 270,065.

the coke will be hard, light and s ongy with large cells but of little strengtli and will break into small pieces when discharged from the oven. lVith too great a proportion of mert matter, on the other hand, the coke will be weak and granular with an insuflicient development of cell structure.

The commercial requirements as to the quality of coke vary with its different applications. Thus, while a good cell structure and some degree of both hardness and toughness are required in all cases, for some uses, as in iron blast furnaces, hardness is the more important in order that the coke may properly resist the action of the oxidizing atmosphere in the upper part of the furnace, whereas in other cases, as in foundry cupolas, for example, it is more important that the coke shall be in large pieces and shall have a high degree of toughness in order that it may not be broken by the heavy pieces of iron in the cupola and ,thus become compacted so as to resist the passage of air and gases.

It has heretofore been the practice, in order to produce coke adapted to specific uses, to mix together coals containing different proportions of the coking substance. While this is attended with a certain degree of success, the bringing together and mixing of different coals and the keeping on hand of different stocks is a source of difficulty and expense. It has been attempted also to compensate for a deficiency of the coking substance in the coal by adding pitch as a substitute therefor. But while this increases the hardness of the coke, it has the disadvantage of, at the same time, reducing its toughness. So also it has been attempted to remedy the opposite condition, 7'. 0., a deficiency in the inert matter-in the coal, by adding coke breeze to the coal before coking. But while this increases the toughness of the coke it, at the same time, decreases its hardness. But in the development of the art up to the present time there has not been full recognition of the principle that certain coals, while otherwise suited for the production of coke. are deficient in the coking substance, or that the coking substance is of inferior quality to produce the best coke structure, or that there is a deficiency in the percentage of inert matter which is quite as necessary to the production of the proper coke structure as is the coking substance,

and thatthese deficiencies maybe reinforced by the addition to the coal mixture, in the correct proportion, of other substances to make up the deficiency found in the coal mixture of either quality or amount of the coking substance, or in the amount of inert matter, as the case may be, or a combination of these additions as experiment showsthem to be needed.

I have found by a study of many coals and in "the light of a full recognition of these several deficiencies, and my invention is based on the discovery that while the addition of pitch to coal decreases ,the toughness of the coke produced, such decrease 1s.

less than the increase in hardness, and that while the addition of coke breeze decreases the hardness of the coke, such decrease is less than the resulting increase in toughness and that therefore by adding to a coking coal both pitch and cokebreeze in proper proportions a coke having the deslred quallties of hardness and toughness in such a degree as to best fit it for the use to which it is to be applied can be produced, the weakness incident to the introduction of each substance being corrected by theother, while the effects oiboth in increased hardness and toughness are retained.

To illustrate the foregoing there are given below figures showing results of tests to determine size and toughness of cokes made,-

first, from a mixture of coals which experiof coke remaining on a screen with 4: square openings; that of toughness in percentage of coke remaining on 3 square screen in the standard shatter test method of de termining the strength of coke.

(3.) Sameas 2 (2.) Same with an ad icoel with tional 2% per (1.) Coalalone. Bpercent. cent. breeze breeze and 2 er added. cent. pi ch added.

Size test: Per cent.

on 41 59 66 Shatter test: Per

cent. on 3 34 52 58 The results of these tests very clearly indicate that both the average size of the pieces and their toughness have been materially improved.

In carrying my invention into efi'ect, I use preferably solid pitch which is pulverized to such an extent that 80 per cent. will pass through a screen havmga inch openings and not less than 95 per cent. through a screen having inch openings. The breeze employed is'of substantially the same size and both are thoroughly mixed with the coal before coking, in proper proportions. But I do not confine my invention to the use of these sizes, or to any degree of hardness of the pitch.

The proportion of pitch and breeze to be employed in any given case must be determined by experiment, having reference to the proportion of natural coking substance in the coal employed, the rate at which it is desired to coke the coal mixture, and the use to which the coke is to be applied 2'. e., to the relative degrees of hardness and toughness desired. Such tests can be readily made in ways well understood by those 'skilled in the art. 1

Evidently to coals having an excess of the coking substance a greater percentage vof coke breeze will be added and conversely to those deficient in the coking substance a greater proportion of pitch.

In general terms the formula of the mixture of pitch and breeze to be added to the coal may be defined as follows: first such proportion of either pitch or coke breeze as may be required with the coal employed to produce a coke having the qualities of toughness and hardness in equilibrium and such additional proportions of both pitch and coke breeze as may be required to produce a coke having the desired degree of toughness and hardness. Ordinarily such additional proportions of pitch and breeze will be about 3 per cent. of hard pitch and from 4 to 5 per cent. of fine breeze, although these proportions are subject to modification according to. the quality of coke to be produced. The mixture when formed is subjected to a coking temperature in a closed retort or oven in the usual manner.

My invention besides enabling the production of coke of good cellular structure and of any practical degree of toughness and hardness, also presents certain other commercial advantages. Thus, in the manufacture of foundry coke in by-product ovens, it is ordinarily necessary to operate the ovens comparatively slowly in order to produce the tough blocky pieces required by the trade. I find, however, that when pitch and breeze have been added in accordance with the specified requirements, the coal can be coked much more rapidly and still produce coke having the desired characteristics; thus enabling the plant to be worked to better advantage.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is 1. The process of regulating the quality of coke which consists in adding to the coal to be coked such proportion of dry pitch or coke breeze as will correct the excess or deficiency of the coking substance 'in the coal and such additional proportions of pitch and breeze as will give to the coke to be produced the desired degree of toughness and hardness and coking the mixture.

2. The process of regulating the quality of coke which consists in adding to the coal to be coked according to its quality such 10 roporti n of pitch or coke breeze as will cause the coke to be produced to have the qualities of toughness and hardness in equilibrium, and such. additional proportions of both pitch and coke breeze as will give to the coke the desired degree of toughness and hardness and coking the mixture.

In testimony whereof I have aflixed my signature,.this 26th day of December, 1918.

WALTER L. GRAUL. 

